I think we had a thread about a year ago on how to make your own
penetrating oil that I can't find with Google. I've been using
gallons (literally) of PB Blaster at $3.90-4.50/can. The stuff really
works great andI'm a staunch advocate of it. However, I'd like to try
a tank vs. using tons of cans spraying small parts that are often off
cars/machines already.

Would people mind posting their favorite formulas again? I'd like to
make a dip tank of the stuff (meaning a couple of gallons for small
parts) plus brush it on when I don't need an aerosol.

One formula I found using Google is:
1/3 no odor space heater kerosene
1/3 no odor mineral spirits
1/3 any weight oil you have around

I find the most effective is to try to pump the oil into the crevices
using heat.
Heat to over the boiling point of the solvent, dip in oil, repeat.
This causes the air and water vapour to diffuse out as it's exposed
to the solvent vapour.
Repeat a couple of times, and it will free quite a lot of stuff.